There are many known industrial processes that require the use of carbon monoxide principally in the production of chemicals including the manufacture of aldehydes, methanol, phosgene and acetic acid via the MONSANTO process. Carbon monoxide is also hydrogenated to liquid hydrocarbon fuels in the Fischer-Tropsch process. A common manner of producing such carbon monoxide is through steam methane reforming and the separation of carbon monoxide from resulting synthesis gases in connection with the production of hydrogen.
Hydrogen has also been produced by natural gas assisted steam electrolyzers in which steam is contacted at the cathode side of an electrically driven oxygen separation devices to produce hydrogen from the disassociation of water that is assisted by combustion of natural gas at anode side of the separation device. An example of such a device is shown in U.S. Pat. No. 6,051,125. It is to be noted that such devices are similar to fuel cells save the fact that instead of generating electricity, a voltage is applied to drive the oxygen ion transport.
Typically, such electrically driven oxygen separation devices have a membrane element that incorporates an electrolyte layer to conduct oxygen ions that is located between two electrode layers to apply an electrical potential across the electrolyte. The electrode layers are porous and can have sublayers while the electrolyte is an air-tight, dense layer. The resulting composite structure can be in the form of a tube in which the oxygen containing feed is fed to the inside of the tube and the separated oxygen is either collected on the outside of the tube and then dissipated. The reverse is possible and oxygen can be fed to the outside of the tube and the permeated oxygen collected on the inside of the tube. Other forms are possible, for example, flat plates and honeycomb-like structures.
The electrolyte layer is formed of an ionic conductor that is capable of conducting oxygen ions when subjected to an elevated operational temperature and an electrical potential applied to the electrode layers. Under such circumstances, the oxygen ions will ionize on one surface of the electrolyte layer known as the cathode side and under the impetus of the electrical potential will be transported through the electrolyte layer to the opposite cathode side where the oxygen ions will recombine into molecular oxygen. Typical materials that are used to form the electrolyte layer are yttria stabilized zirconia and gadolinium doped ceria. The electrical potential is applied to the electrolyte by way of cathode and anode electrodes. The oxygen ionizes at the cathode and the oxygen ions recombine at the anode. Typically, electrodes can be made of mixtures of the electrolyte material and a conductive metal, metal alloy or an electrically conductive perovskite. In order to distribute current to the electrodes, current collectors are utilized in the form of layers on the electrodes opposite to the electrolyte.
As will be discussed, the present invention provides a method of generating carbon monoxide from a carbon dioxide containing feed with the use of an electrically driven oxygen separation device.